Flexible coating materials have attracted much attention for the surface functionalization of biomedical devices. In this work, one cationic coating material (AQTA) is constructed with the co-substitution of tannic acid with alkyl and quaternary ammonium groups, and then employed to functionalize versatile medical devices for antibacterial and hemostatic applications. Stable AQTA coatings with tunable contents are realized by facile onestep soaking process, owing to the well-designed molecular structure of AQTA (elaborate combination of long chain alkyl, phenolic hydroxyl and quaternary ammonium groups). The high content of AQTA is coated on polyurethane (as the model substrate of medical catheters), which achieves high blood compatibility and in vitro/ in vivo antibacterial ability. The feasibility of AQTA for hemostatic uses is confirmed by the improved properties of functionalized alginate dressing and gauze with one moderate content of AQTA. Together with the negative role of AQTA on the hemostatic performance of chitosan dressing, the underlying hemostatic mechanism of AQTA for negatively charged dressings was revealed as the optimized surface-activated platelet adhesion. Two typical rat-hemorrhage models further confirm the high hemostatic performance of AQTA-coated dressing. This work sheds light on the design and flexible management of cationic coating materials for biomedical applications.